Method for electrostatic coating of objects with a powder coating material

ABSTRACT

THE PRESENT INVENTION RELATES TO A METHOD AND APPARATUS FOR THE PARTIAL SURFACE COATING OF OBJECTS, SUCH AS ELECTRICAL COMPONENTS, MOVING PAST AN ELECTROSTATIC COATING STATION WHERE THEY ARE COATED WITH ELECTRIFIED PARTICLES OF COATING MATERIAL. ACCORDING TO THE INVENTION THE PORTION OR PORTIONS OF THE COMPONENTS WHICH ARE NOT TO BE COATED, E.G. THE CONNECTING WIRES OF ELECTRICAL COMPONENTS, ARE MAINTAINED IN A ZONE OF PNEUMATIC OVERPRESSURE DURING THEIR PASSAGE THROUGH THE COATING STATION, WHEREBY SUCH PORTIONS DO NOT BECOME COATED.

Oct. 3, 1972 FABRE EI'AL 3,695,909

METHOD FOR ELECTROSTATIC COATING OF OBJECTS WITH A POWDER COATING MATERIAL Filed May 18, 1970 4 Sheets-Sheet l Oct. 3, 1972 P. FABRE ETAL METHOD FOR ELECTROSTATIC COATING 0F OBJECTS WITH A POWDER COATING MATERIAL 4 Sheets-Sheet 2 Filed May 18 1970 Oct. 3, 1972 P FABRE ETAL 3,695,909

METHOD FOR ELECTROSTATIC COATING 0F OBJECTS WITH A POWDER COATING MATERIAL Filed May 18, 1970 4 Sheets-Sheet 3 Oct. 33,1972 P. FABRE ETI'AL 3,695,909

METHOD FOR ELECTROSTATIC COATING OF OBJECTS WITH A POWDER COATING MATERIAL 4 Sheets-Sheet 4 Filed May 18, 1970 Unitcd States Patent 3,695,909 METHOD FOR ELECTROSTATIC COATING OF OBJECTS WITH A POWDER COATING MATERIAL Pierre Fahre, Grenoble, Robert Giroud-Garampon, Vourey, Michel Gondrand, Grenoble, and Fernarld Raymond, Meyland, France, assignors to 'Ihnzmi Ameliorair Thermique, Aeraulique, Mecanique (T.A.M. Paris, France Filed May 18, 1970, Ser. No. 37,971 Claims priority, applicagtitgaolgrance, May 23, 1969,

Int. Cl. 344d 1/094, 1/095; B!) 5/02 US. Cl. 11717.5 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a method and apparatus for the partial surface coating of objects moving past an electrostatic coating station, and more particularly a powder coating station producing a cloud of electrified powder particles.

Apparatus of this type is presently used in order to obtain the coating of objects with a powder which is then melted or fused, so as to form a continuous film and to ensure a uniform protective or decorative coating. In numerous applications, and more particularly in the case of electronic components comprising a body associated with connection conductors, it is essential that the coating does not extend onto these electric conductors, or at least extends only partially thereon so as not to prevent a good connection contact.

Hitherto, such a coating process has been carried out by elfecting total coating of the electronic components which is followed by partial removal of the powder by limited blowing at the place of the connection conductors. This method entails a supplementary and unsatisfactory operation, in the sense that a small number of particles which are strongly attached to the conductors are not eliminated, so that the final electrical connections have uuallowable faults due to these particles which have melted with those coating the body of electronic components.

It has also been proposed to place covers and at times, covers under slight over-pressure, at the locations on the objects which do not have to be coated, but this arrangement does not always give complete satisfaction and is not applied to partial coating of objects continuously passing a coating station.

The present invention aims to reduce or overcome these drawbacks and provides a method and apparatus wherein the partial superficial coating of objects passing a coating station is ensured in a particularly clean manner, without any depositing of particles on the portions of the objects which are not to be coated thereon.

The method according to the invention is characterised in that at least one elongated zone is created under slight pneumatic over-pressure and free from any particles, the said zone extending through and across the said cloud of particles, and a portion not to be covered of each object is constantly within the zone under slight over-pressure.

3,695,909 Patented Oct. 3, 1972 Apparatus using this method and applied to objects being carried on a conveyor comprises, at the location of the electrostatic coating station, at least one elongated enclosure for a zone under slight over-pressure, having at least one longitudinal opening parallel to the direction of displacement of the conveyor. '][n this way, the portions not to be coated of the objects travelling past the coating station are located through the opening or openings, whilst the portions to be coated pass through the zone subjected to the effect of the electrostatic powder.

The invention will now be further described, by way of example, with reference to the attached drawings in which:

FIG. 1 is a perspective view, having portions broken away, of one embodiment of coating apparatus according to the invention,

FIG. 2 is a transverse section. through the apparatus of FIG. 1;

FIG. 3 is a partial sectional view of a further embodiment of apparatus according to the invention; and

FIG. 4 is a partial sectional view of yet another embodiment of apparatus according to the invention.

Referring to FIGS. 1 and 2, the coating apparatus comprises a fiuidisation tank 1, formed in a manner known per se, having a porous bottom 2, associated with electrification means 3, and an intake 4 for fluidisation air. The powder which is deposited above the porous bottom is fluidised within a chamber 5, and is attracted towards the objects to be coated, which are maintained at earth potential, by the effect of the electric field. The apparatus also comprises two elongated boxes forming longitudinal enclosures 6 and 7, each formed from a member 8 of parallelepipedal form having a narrow opening 9 extending from end to end, according to the direction of displacement of a conveyor. Each of the enclosures 6 and 7 is connected to at least one air inlet pipe 10 which slight- 1y over-pressurizes the enclosures 6 and 7.

The objects 11 to be coated are shown herein as resistors, capacitors or other electronic components, and comprises a body 12 and lateral conductors 13 and 14. These components are attached, at the ends of the conductors 13 and 14, to lateral bands 15, 16 forming conveyor belts, and during their passage across the coating station, these conductors 13 and 14 rest on the lower edge 17 defining the lower longitudinal portion of each opening 9.

It will be noted that input and. output screens 18 and 19 are positioned on the chamber 5, the boxes 8 forming the pressurised enclosures extending on both sides of the fluidisation chamber beyond its input and output screens.

Thus, during the passage of the electronic components 11 through the fluidised bath, the air admitted into each of the enclosures 6 and 7 causes slight over-pressure in these enclosures which avoids any introduction of particles into the said enclosures and consequently any depositing of particles on the part of the conductors 13 and 14 which is situated within the said enclosures 6 and 7. On the contrary, the depositing of coating material on the body 12 of the electronic components 11 is not disturbed.

Referring to FIG. 3 there is shown a pneumatic and electrostatic spray nozzle 20 of a type known per se, which sprays a current of air 21 transporting particles of powder in the direction of the electronic components 22 whose conductors 23 and 24 are inserted into pressurized enclosures 25, 26, which are supported by pillars 27 and 28. It will be noted that the lower edge 29 of the openings is recessed so that the openings do not face the powder station, but in a direction such that the path of the particles towards an enclosure follows a meandering course terminating in an upward direction, which is advantageous. An aspirator 30 is located below the sprayed cloud and allows recovery of the particles not deposited.

Referring now to FIG. 4, each enclosure 41 under slight over-pressure, as in the embodiments of FIGS. 1 and 2, is formed at the side of the coating sation above and below by double walls 43 and 44 thereby defining two flat conduits 45 and 46 discharging at the location of the opening 47, these conduits communicating with narrow chambers 48 and 49. The chamber 48 is under pressure whilst the chamber 49 is kept at subatmospheric pressure by means of an air supplying duct 51 and an air extracting duct 52 respectively, so that an extended jet of air is issued from the conduit 45 across the opening 47 and is collected by the conduit 46. A curtain of air is thus formed, as shown by the arrows 1, very clearly separating the area of the enclosure under slight over-pressure from the outer space wherein the cloud of electrified powder particles is located. Advantageously, one or more vibrators 50 are arranged on the enclosure 41, and preferably adjacent each upper wall defining the opening, which prevents the powder from collecting on these walls.

The invention applies to the coating of objects not only by electrostatic powdering but also by electrostatic paintmg.

We claim:

1. Method of continuously applying a partial surface coating to objects by passing said objects through a cloud of electrified particles of a coating product, which method comprises the steps of maintaining at least one elongated zone adjacent said cloud under a gaseous pressure higher than that prevailing within said cloud and free of any particles, the said zone extending in the direction of displacement of the objects to be coated, and passing said objects through said cloud with a portion of said objects not to be coated within said zone under higher pressure.

2. Method as claimed in claim 1 which comprises the step of establishing a curtain of air extending laterally of said zone in said direction of displacement, which curtain separates said zone from said cloud substantially at the region of separation between the portion of said objects to be coated and the portion which is to remain uncoated.

3. Method as claimed in claim 1 which comprises the step of maintaining said zone within an elongated enclosure having a longitudinal opening extending in said direction of displacement, through which opening the portions of said objects to remain uncoated project into said zone.

4. Method as claimed in claim 1 in which said objects are electronic components comprising connective conductors extending at least partially into said zone under higher pressure.

5. Method as claimed in claim 1 in which said cloud is a fluidized bed.

References Cited UNITED STATES PATENTS 3,296,999 1/1967 Gamble l17-38 1,964,790 7/1934 Roberts 118-301 2,505,063 4/1950 Palermo 1l743 3,318,281 5/1967 Plegat 118-301 3,377,183 4/1968 Hurt et a1 117-38 2,721,535 10/1955 Zitkus 118-301 3,310,431 3/1967 Loose 117----65.2 3,521,557 7/1970 Fisher et a1. 117-17.5 3,526,027 9/1970 Manuel et a1. 1l7--17.5

FOREIGN PATENTS 418,903 8/1966 Switzerland 11793.4 R

1,081,368 5/1960 Germany 118-504 ALFRED L. LEAVITT, Primary Examiner I. H. NEWSOME, Assistant Examiner US. Cl. X.R. 

